High speed cutting of any material can be effected by many arrangements between the cutter and the material being cut. However, there are certain limitations found in high speed cutting. For example, it has been noted that the greater the differential in the directional speed of the cutter relative to the directional speed of the material being cut, the poorer will be the quality of the cut in the material. If the object is to minimize poor quality cutting in a material, then it is desirable to minimize this differential in directional speed. Heretofore, this has been accomplished by reducing the directional speed in the material being cut. This, of course, materially increases the cost of the cutting operation.
Omnidirectional cutting means have the capacity of cutting in any direction. They have been utilized as fixed, reciprocating, oscillating, and pattern-following cutting means. They add a significant degree of versatility to the commercial cutting of a wide array of materials.
Omnidirectional cutting can be accomplished by a number of techniques including waterjet cutting, laser machining and cutting/routing (hereinafter called "omnidirectional cutters"). These techniques have been used where either the piece that is being cut is moved or the omnidirectional cutting means is moved. There are known processes where both are moved in linear or essentially linear directions. For example, the cutter is moved essentially laterally of the piece or the omnidirectional cutting means is oscillated within a small arc laterally into a linearly moving piece. To date, the art has not employed an omnidirectional cutting means where the object being cut is linearly moved and the cutting means is arc-directed into, across and in the direction of the object to effect an arc-defining cut, such as a slit, in the object.
Many of the materials which are subjected to omnidirectional cutting are batch fabricated and cutting of them is likewise a batch operation. Omnidirectional cutting has been used to configure and shape an article. If the cut in the object is complex, and the object is large, it is logical to find a way of moving the omnidirectional cutter across the material to generate the desired shape. See Francis, U.S. Pat. No. 2,736,349, patented Feb. 28, 1956, Wiatt, et al., U.S. Pat. No. 3,350,969, patented Nov. 7, 1967, Wiatt, U.S. Pat. No. 3,347,121, patented Oct. 17, 1967, and Lange, et al., U.S. Pat. No. 3,950,189, patented Apr. 13, 1976. However, if the object is relatively small and the cut is complex, then the object being cut would be manipulated and the cutting means would be kept in a stationary position. See PM&E, Jul. 1986.
There are materials such as plastic film, metal sheeting and textiles that are produced in continuous runs. There are situations when an arc-like cut is desirable in such materials. Heretofore, this has been accomplished by the use of reciprocating or oscillating cutting devices which fail to follow in the direction of the movement of the object being cut. If the cutting motion of the omnidirectional cutter is a straight line, as occurs when the cutter is moved in a straight-line reciprocating motion, and the continuous run of material is supplied in a rectilinear fashion, the resulting lateral cut into the material will be curved and the degree of the curve will depend on the relative speeds of the reciprocating cutter and the continuous run of material. Essentially the same patterns are obtained or obtainable when the omnidirectional cutter is oscillated across and into the rectilinearly moving material. An oscillating cutter is essentially the same as a reciprocating cutter. The differences between these techniques is that the reciprocating cutter travels a clearly rectilinear path while the oscillating cutter generates an arc path motion invariably against the direction of the material being cut. There is an obvious limitation on the design of the cut one may effect by such processes. See Litzka, U.S. Pat. Nos. 3,066,394, patented Dec. 4, 1962, Francis, U.S. Pat. No. 2,736,349, patented Feb. 28, 1956, Wiatt, et al., U.S. Pat. No. 3,350,969, patented Nov. 7, 1967, Wiatt, U.S. Pat. No. 3,347,121, patented Oct. 17, 1967, Kloehn, et al., U.S. Pat. No. 4,567,796, patented Feb. 4, 1986, and Kloehn, et al., U.S. Pat. No. 4,573,382, patented Mar. 4, 1986.
Reciprocation or oscillation of an omnidirectional cutting means rapidly into and out of an edge of a moving sheet of material produces a slanted slit having a gentle arc until the apex portion which is an abrupt curve that generates a parabolic slice defining a sharply formed or narrow apex (or tip). If such techniques are employed to effect a parabolic cut through a folded edge of a plastic or paper sheet, the unfolded sheet will not be an ellipse, but rather two (2) parabolas joined to form a hole and each juncture is an angle of about 30 or greater. At maximum line speed, this type of reciprocating cutting motion will typically create a poor quality cut because the cutting speed exceeds the speed at which the cutting stream most effectively cuts the material and because of the dynamic loads imposed on the cutter in the course of rapid cutter reciprocation which causes splaying of the cutter means during the turnaround. Kloehn, et al., U.S. Pat. No. 4,567,796, patented Feb. 4, 1986, and U.S. Pat. No. 4,573,382, patented Mar. 4, 1986. In order to vary the kind of cut performed by such cutters, it is necessary to cause them to alter their motion during the cutting action. This introduces complications in the mechanics of their operation. U.S. Pat. No. 4,573,382 is directed to the oscillating waterjet cutting of plastic sheeting to make leg holes in baby diaper constructions. The patent oscillates a cutter into the sheeting and with cam arrangements varies the cutter's motion within the sheeting to elongate the hole that is cut. Such a cutting operation can impart high dynamic loads on the nozzle of the cutter which imposes stress on the cam system controlling the nozzle's movement. According to the patent, at col. 4, lines 13 et seq., cam means are put under great stress when used in oscillator waterjet cutters and "these stresses seriously limit the speed at which the web 6 can be cut. . . " To "minimize," but not necessarily overcome the problem, a "compromise cutting line" for the fluid jet is followed. Such apparently results in a compromise in the achievable cutting patterns, exhibiting the limitations of a process that places undue stress on the apparatus.
Thus, reciprocating and oscillating cutting means, whether omnidirectional or not, have limitations as to rate of production and quality of the cut formed. This point is further illustrated by the following:
U.S. Pat. No. 4,624,654, patented Nov. 25, 1986 to Boyd, et al., describes a method and apparatus for manufacturing draw-tape bags. Included in the method of the patent is a step in which holes are provided in a hem portion of the bag. The patent describes this feature in the following manner (see column 2, lines 15-24).
"Yet another important aspect of the invention is that holes are provided in each hem between the folding and inserting steps so as to expose the subsequently inserted strip. In the described embodiment, the holes are cut at regular intervals along each hem as the material is continuously advanced between the folding and inserting steps. In particular, holes are punched simultaneously in the longitudinal fold edges of the hems as the material is continuously advanced." PA0 "The punch 28 forms a hole in the longitudinal edge of each hem. These holes are depicted in FIG. 5, the holes 44 and 46 being formed in the longitudinal edges 20' and 22' of the hems 40 and 42 respectively. Because the holes 44 and 46 are formed by removing a portion of the edge of each hem, a conventional reciprocating punch 28 can be used to cut holes 44 and 46 simultaneously through the two hems in a single descending motion. Because it is pliable, the advancing material simply bends or deflects around the descended punch until the punch withdraws. The rate of the punch 28 is coordinated with the film advance rate of the pinch rollers 24 to form holes 44 and 46 at regular, one bag pitch intervals along the length of the advancing film 12."(Emphasis supplied)
The cutting of the hole is effected by a reciprocating punch. The patent describes this step in the following manner (see column 4, lines 4-17):
This patentee depends, in forming the hole, on the pliability of the plastic being cut. The patentee depends on the bending and deflection of the plastic around the descended punch until it is withdrawn. This is a clear indication that the rate at which the film can be advanced has to be limited by the rate of the hole puncher and the pliability of the material being punched. If the material were not as pliable as the bag materials the patentee was cutting, then, of course, take-up rollers would have to be included in the line before the cutters, and tensioning rollers would have to be employed after the cutter in order to accommodate the stop motion required by the cutting action. However, in the case of the patent, the dependence upon the pliability of the plastic to allow hole cutting without stopping the movement of the film results in a very coarse looking cut pattern in the plastic. In any event, the reciprocating puncher introduces a stop motion into the process where the plastic is continuously advanced.
It would be desirable to be able to effect a repetitive pattern of an arc cut in a continuous run of a recipient surface without having to slow or stop the run or without altering the direction of motion of the cutting means or without depending upon the pliability of the recipient surface to take up the stop motion or slow down in motion which is inherent in the utilization of such reciprocating cutters or punches.
It would be desirable to effect an arc cut in a sheeting material which is not limited by stresses imposed on the cutting means because of reciprocating or oscillating motions.
This invention is directed to a process and apparatus for making an arc cut in a sheeting material which avoids the disadvantages of this prior art.